These studies are designed to evaluate the control of intestinal ion secretion with emphasis on the mechanism by which several agents induce intestinal electrolyte secretion, and on the identification of different agents which may inhibit intestinal electrolyte secretion. Additional studies are planned to define the mechanism by which lithium inhibits cholera enterotoxin induced secretion in rabbit ileum. Our present results are consistent with the hypothesis that lithium partially inhibits cyclic AMP mediated ion secretion by stimulating mucosal cyclic nucleotide phosphodiesterase activity. Studies will directly test this hypothesis by measuring cyclic nucleotide phosphodiesterase and adenylate cyclase activity. The effect of both catecholamines and several gastrointestinal hormones on colonic ion transport will be continued. We have to date demonstrated that vasoactive intestinal polypeptide stimulates electrolyte secretion in the colon and are presently evaluating the effect of secretin, cholecystokinin and epinephrine on ion transport. Finally, studies are planned which will evaluate the mechanism of oxalate absorption in the small intestine and the mechanism of hyperoxaluria in patients with intestinal disease.